The present invention relates to phased array radar systems, and more particularly to such electronically steerable systems designed for operation with broadband linear FM signals.
A phased array radar system employs a fixed, generally planar antenna array made up of individual or subarrays of radiating elements. The radiation pattern generated has a shape and direction which is determined by the relative phases and amplitudes of the currents at the individual radiating elements. The relative phases of the outputs from the individual radiating elements are varied to electronically steer the beam. A general description of electronically steered phased-array radar systems can be had from, "Introduction to Radar Systems", by M. I. Skolnik, 2nd ed. 1982, McGraw-Hill.
A phased array antenna beam steering controller is taught in U.S. Pat. No. 4,217,587, owned by the assignee of the present invention. A highly linearized FM waveform generation system is taught by U.S. Pat. No. 4,160,958, also owned by the assignee of the present invention. Such a linear FM waveform generator can provide wideband waveforms for phased array radars.
It is well understood that phased array radar antenna systems must use some form of time delay mechanism to hold a radiated beam in a constant spatial position when using a broadband signal. This is illustrated in FIG. 1 of the drawings. Mechanizing broadband time delay elements for a phased array radar antenna is a difficult problem. The total time delay required is determined by the array size, and for a 10 foot array steering .+-.60 degrees, the outer array elements need selectable time delay of up to 10 nanoseconds, while the inner elements need up to 5 nanoseconds. Such time delay elements built using conventional microwave techniques tend to be physically large and awkward, and lossy, and have a very limited power handling capability. It is generally not feasible to drive significant amounts of transmitter power through such time delay elements.
A wideband phased array radar antenna system is taught by U.S. Pat. No. 4,263,600. This prior art system seeks to phase shift the full wideband signal which is applied directly to the phase shifters. This system would be very difficult to implement due to phase shifter hardware limitations for handling the wideband signal.
The present invention is directed to providing a solution to the time delay steering problem for use with wideband linear FM waveform, phased array antenna systems. This solution employs conventional hardware to generate a synthetic time delay.